Slurry polishers are well known in the art and are also well known for use in planarizing deposited layers on semiconductor wafers. For example, U.S. Pat. No. 5,055,158 discloses a use of slurry polishing in the manufacture of Josephson integrated circuits where a deposited dielectric material is planarized so that additional layers can be deposited.
Typically, a slurry polisher comprises a rotating horizontal pad covered by a layer of polishing slurry. The workpiece, typically a semiconductor wafer, is pressed against the rotating pad and polishing results. The wafer itself is usually rotated at a slower rate than the pad and may also be moved radially back and forth across the rotating pad to equalize material removal from the wafer surface.
The material of the polishing pad is chosen for its ability to act as a carrier of the slurry and to wipe away the grit and debris resulting from the polishing action. One particular pad material is described in U.S. Pat. No. 4,927,432.
A typical application of slurry polishing on semiconductor wafers is to planarize a deposited layer on a wafer. For example, after a number of processing steps, such as masking, doping, etching and the like, have been performed on the wafer, the surface of the wafer can become uneven. It may be necessary to smooth out the surface for subsequent processing steps. For this purpose, a layer of insulating or dielectric material, e.g. silicon dioxide, can be deposited on the uneven surface and then polished to obtain the desired smooth surface. It is clear that such polishing operations must be carried out in such a way that scratches or other defects do not appear on the polished surface and that the material removal should preferably be extremely uniform across the surface. Unfortunately, after a period of use, a slurry polishing pad deteriorates and must be replaced. Polishing with a deteriorated or worn pad causes more scratches and other defects as well as surface non-uniformities.
One drawback to the use of slurry polishing is that the polishing pads may have to be replaced more than once in a factory shift, which causes production bottlenecks when the polishing machine has to be taken out of use for such replacement. It is therefore desirable to find a way to prolong the life of such polishing pads to at least a full shift.